This invention relates to new and useful improvements in apparatus used to determine the air content of fresh concrete and in particular to determine the air content of fresh concrete containing normal and lightweight aggregate.
It is well known that proper use of entrained air in concrete can produce significant improvements in important properties such as workability in fresh concrete and frost resistance in hardened concrete.
Conventionally, a number of test methods have been developed to determine this air content and four such methods are in current use. These include pressure tests, gravimetric tests, volumetric tests for fresh concrete and microscopic linear traverse or point count methods for hardened concrete.
It has been found that only the volumetric method is suitable for use with both lightweight and normal density fresh concretes and is also suitable as a controlled test in the field.
However the major drawback of the present volumetric method is the relatively large sample size required, namely, 0.075 ft..sup.3 (2.1 liters).
When this weight of concrete sample is combined with that of the apparatus, it requires considerable physical effort to carry out the mixing which is so necessary to perform the test.
Other prior art known to applicant is listed below:
PRIOR ART
U.S. Pat. No. 2,635,459, Chesleigh Gray, issued Apr. 21, 1953. This comprises a cylindrical container with a conical cover securable to the container with the cover having various ports therein one of which permits pressurization of the interior. The device also is designed to measure the percentage of surface moisture on saturated discrete material.
U.S. Pat. No. 2,668,437, O. G. Patch, issued Feb. 9, 1954. This also is a pressure type apparatus as is the previous patent and of course requires a source of air and pressure.
U.S. Pat. No. 2,722,825, E. V. Meyer, issued Nov. 8, 1955. In this patent, the concrete is placed in the main container and includes a scale in which the zero point is situated near the top of a rod. The height of the sample now has to be determined by sighting along the top edge of the container and reading the scale on the rod. It will be noted that the container is not filled with concrete hence the requirement for this measurement.
U.S. Pat. No. 2,892,343, L. M. Chace, issued June 30, 1959. This is a volumetric apparatus utilizing a barrel and cup with a stopper at one end.
U.S. Pat. No. 4,344,316, K. W. Nasser (present applicant), issued Aug. 17, 1982. This discloses a chamber having an open end and an opposite closable end and provided with a heating device and pressure measuring device.
Publication: Mini Air Meter For Fresh Concrete by K. W. Nasser and B. D. Whaley, Concrete International, March, 1988 pp. 43-46.
The present invention overcomes disadvantages inherent with the prior art and present methods and in accordance with the invention there is provided apparatus for volumetrically determining the air content of fresh regular or lightweight concrete comprising in combination a base container, a concrete sample holding bowl detachably engageable within said container, with the upper side of said bowl being situated below the upper side of said base container, a cover component, said cover component including a hollow lower body portion selectively engageable in sealed relationship upon said base container, a hollow conical upper portion extending upwardly from said lower body portion and a vertically situated conduit extending upwardly from the apex of said conical upper portion and communicating with the interior thereof and a cap detachably and sealably engageable upon the upper end of said conduit.
Another aspect of the invention discloses a method of determining the entrained air content of fresh regular or lightweight concrete utilizing the apparatus according to claim 1, which comprises the steps of:
a. filling said concrete sample holding bowl with fresh concrete substantially flush with the upper side edge thereof;
b. rodding said concrete to eliminate substantially, relatively large entrapped air voids therein;
c. placing said bowl within said base container and filling said base container with water and flooding the upper surface of the concrete within said bowl;
d. sealably locking said cover component onto said base container;
e. filling said cover component with water up to the top of said conduit, and sealably engaging said cap upon the upper end of said conduit;
f. thoroughly agitating said apparatus to release substantially all entrained air in said fresh concrete sample;
g. placing said apparatus upright upon a supporting surface and removing said cap to release said entrained air;
h. topping up the water within said apparatus with an anti-foaming liquid to replace the released entrained air and measuring said liquid; and
i. calculating the amount of escaped entrained air in said concrete sample from the amount of liquid added.
Another advantage of the present device is to provide a relatively simple apparatus based on the volumetric method to determine the air content of fresh concrete both regular and lightweight concrete. The results show that this device is reliable, easy to operate and portable enough for both field and laboratory use.
A still further advantage of the present invention is to provide a device and method of the character herewithin described which is simple in construction, economical in manufacture and otherwise well suited to the purpose of which it is designed.
With the foregoing in view, and other advantages as will become apparent to those skilled in the art to which this invention relates as this specification proceeds, the invention is herein described by reference to the accompanying drawings forming a part hereof, which includes a description of the best mode known to the applicant and of the preferred typical embodiment of the principles of the present invention, in which: